DOT4 Brake Fluid after 1 Year

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Jul 2, 2019 | 11:38 AM

#31

TheGrandPoohBah

Extreme HDF Member

Joined: Jun 2011

Posts: 14,731

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From: Mountain Top, Alabama

Unless an urgency comes up, I only remove my reservoir covers on low humidity days.

Jul 2, 2019 | 01:19 PM

#32

TheITMercenary

Former Sponsor

Joined: Jan 2019

Posts: 162

Likes: 16

From: WA

Quote:

Originally Posted by RIPSAW

Just out of curiosity, did you calibrate it from a sealed bottle of DOT 4?

The system is sealed. The diaphragm in the master is how it works. Not sure how it could have got that much moisture unless it started with a lot.

If you don't have a moisture checker. You can use your Volt/Ohm meter set high on 10 Meg ohm reading. Put the two probes into the fluid. Takes a few minutes but if it moves up past 5 MG ohm resistance, there is little moisture.

https://www.youtube.com/watch?v=eYOeOTUPbyA

"Sealed" is a relative term. The reservoir gaskets/seals on most modern Harley's are complete garbage. You have to use inch lbs to torque them otherwise they leak (and happily ruin the paint on the cap/reservoir). Beyond that EVERY single Harley I have worked on that uses this system is completely water soaked brake fluid wise after about a year. I just helped a friend with a year old fluid swap (his first was done by the dealer) and it's brown and nasty as can be (read: water).

DOT 4 is hygroscopic.... nature of the beast. Most vehicles have similar issues (though not as fast due to better cap seal designs) though many rarely change/flush auto brake fluid as it "still works".

Jul 2, 2019 | 10:00 PM

#33

hardheaded

Seasoned HDF Member

Joined: Oct 2012

Posts: 11,226

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From: St.Louis Mo.

I'm wondering if you could switch out the dot 4 for dot 5 if you don't have an ABS system ? Use to do this on the old dot 3 systems.

Jul 2, 2019 | 10:57 PM

#34

hattitude

Seasoned HDF Member

Joined: Sep 2008

Posts: 14,165

Likes: 11,257

From: San Diego, CA

Quote:

Originally Posted by hardheaded

I'm wondering if you could switch out the dot 4 for dot 5 if you don't have an ABS system ? Use to do this on the old dot 3 systems.

Sure you could......

I still have two non-ABS Harleys that use DOT5...

The key is to really flush the entire system well, and make sure you get ALL the DOT4 out of the system before adding the DOT 5...

Jul 3, 2019 | 08:16 AM

#35

Rob175

Road Warrior

Joined: Dec 2016

Posts: 1,854

Likes: 944

From: Lincolnshire, IL

Great thread!....it inspired me to order one of those brake fluid testers. Now can someone tell me what I should know about removing the cover and the proper way to replace it and tighten it down correctly (I don't have a tiny torque wrench only a big one)......I do know that brake fuild is corrosive and care needs to be taken not to drip it on any painted surface.....anything else to know??
Thanks.

Jul 3, 2019 | 08:59 AM

#36

Jackie Paper

Seasoned HDF Member

Joined: Mar 2010

Posts: 38,623

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From: Honah Lee

Run screws down till lightly snug and watch side of rubber gasket. Just twerk screws so gasket bulges out slightly. Note that there is a air gap slit on top side between gasket and cover. If you overtighted screws and close this air gap, the bellow will not work. Overtighted, master will also leak.

Do not use master to flush. Vacuum pull it out from calipers and keep vacuum low to prevent air coming around cup seals in master.

System works fine when someone understands it knows what they are doing.

The two year fluid change is most important with ABS and it really requires computer to make it function to bleed. So most with ABS are stuck with dealer service.

Jul 3, 2019 | 09:13 AM

#37

Rob175

Road Warrior

Joined: Dec 2016

Posts: 1,854

Likes: 944

From: Lincolnshire, IL

Thanks "RIP".... I know my level of mechanical ability (or lack of it..LOL) so I won't be doing anything with the brake fluid other than checking the moisture content and replacing the stock cover with a new chrome cover.......all else will be done by my dealer. I've got the 15,000 mile service coming up soon and that's when I'll have them change the fluid. I honestly don't recall them ever changing the fluid during the past 3-1/2 years I've owned my 2015 Ultra Limited. My guess is that it's never been changed and needs to be done next month.

Nov 16, 2019 | 06:26 PM

#38

goldie

Tourer

Joined: Feb 2008

Posts: 403

Likes: 44

From: Montana

Hi all,
I have one of those pen testers and need to understand what is the proper way to check these fluids. My understanding was to only inset the probes about halfway into fluid and not submerge the entire tip. Right or wrong? Some direction would be appreciated.... thanks....goldie